Metallic magnesium is known to react with certain 1,3-dienes yielding halide-free organomagnesium compounds. These reactions are typically catalyzed by alkyl halides or transition metal salts. The dienemagnesium compounds produced from these reactions have been mainly limited to open-chain 1,3-dienes, including 1,3-butadiene, 2-methyl-1,3-butadiene, i.e., isoprene, 1-methyl-3-methylene-1,6-octadiene, i.e., myrcene, 2,3-dimethyl-1,3-butadiene, and (E,E)-1,4-diphenyl-1,3-butadiene.
There are problems associated with the preparation of these reagents using metallic magnesium, however. For example, the reaction of metallic magnesium with 1,3-dienes such as 1,3-butadiene or isoprene usually involves dimerization, trimerization, or oligomerization of the product. Furthermore, the reactions are generally accompanied by a variety of by-products. Consequently, the utilization of these reagents in organic synthesis has been quite limited, except for perhaps the use of 1,3-butadienemagnesium in organometallic synthesis.
It has recently been demonstrated that substituted (2-butene-1,4-diyl)magnesium complexes can be prepared using highly reactive magnesium, produced from MgCl.sub.2, Li, and naphthalene in tetrahydrofuran, and 1,4-diphenyl-1,3-butadiene or 2,3-dimethyl-1,3-butadiene. These halide-free organomagnesium reagents contain two formal Mg-C bonds in one organic species and have been shown to function as bisnucleophiles in reactions with electrophiles. For example, these bis-Grignard reagents formed from 1,3-butadienes react with .alpha.,.omega.-alkylene dihalides in either 1,2-, 1,4-, or 2,1- additions to give complex carbocycles.
Although reactions of highly reactive magnesium with symmetrical 1,3-dienes, specifically, 1,4-diphenyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene, have been shown, reactions with more complex 1,3-dienes have not been discussed to any significant extent in the literature. Thus, it is an object of this invention to prepare (2-butene-1,4-diyl)magnesium complexes from more complex 1,3-diene systems than simple symmetrical 1,3-butadienes such as 1,4-diphenyl-1,3-butadiene and 2,3-dimethyl-1,3-butadiene. Furthermore, it is an object of this invention to utilize such (2-butene-1,4-diyl)magnesium complexes in organic synthesis.